Senators filed a whopping 300 amendments to the bipartisan immigration reform bill this week, setting the stage for intense debate over core elements of the legislation.

The Senate Judiciary Committee will convene on Thursday morning to begin the potentially lengthy process of considering the changes. Most of the amendments come from Republican legislators who oppose the bill. They would carve up some of its central parts, such as the pathway to citizenship, and beef up others, like the border security requirements.

But Democrats have also proposed changes, such as granting same-sex couples equal recognition, that could also challenge the delicate bipartisan coalition that backs the bill.

Judiciary Committee Chairman Patrick Leahy (D-Vt.) said Wednesday that his panel would begin by taking up changes to border-security measures, as well as technical changes.

We read through all 300 amendments. Here are some that could change the makeup of the bill, or at least spark some sexy headlines:

The Dilemma Over Same-Sex Couples

The bipartisan "Gang of Eight" has said they will work together to defeat amendments that could threaten the bill. But a couple of amendments proposed by Leahy may challenge their alliance.

Leahy has proposed an amendment that would allow Americans in long-term same-sex relationships to sponsor their foreign partners for green cards. Another would recognize same-sex unions under immigration law.

Republicans on the "Gang of Eight" have said such changes will "kill" the bill. That puts Democrats on the "Gang" who back gay rights, such as Chuck Schumer (D-N.Y.) and Dick Durbin (D-Ill.), in a tough spot. Do they come out in favor of the bill and risk an exodus of potential Republican votes? Or do they oppose the measures and risk angering advocates who have pushed for gay and lesbian couples to be included in the bill.

Undocumented Immigrants Should Never Be Citizens

Rather than waste his time making a path to citizenship more difficult for undocumented immigrants, Ted Cruz (R-Texas) took a more direct approach: ban it.

An amendment submitted by Cruz would keep most undocumented immigrants from ever becoming citizens. That's significantly harsher than current law, which doesn't provide a reasonable pathway to citizenship for most undocumented immigrants, but doesn't specifically ban it, either.

And then there are the senators who will just make things a little harder for undocumented immigrants applying for legalization. Along those lines, Sen. Orrin Hatch (R-Utah) would ask the majority of those applicants to submit a DNA sample along with other data.

An Easier Pathway to Citizenship

Some Republicans want to make it nearly impossible for undocumented immigrants to get citizenship. But several Democrats want to make the path easier.

Sens. Dianne Feinstein (Calif.) and Richard Blumenthal (Conn.) want to do away with the Dec. 31, 2011 cutoff date in the bill. Under the current proposal, undocumented immigrants who arrived after that date are ineligible for provisional legal status, the first step on the path to citizenship. Blumenthal's amendment would move the cutoff date up to April 17, 2013.

Blumenthal also wants to offer undocumented immigrants under the age of 18 the same, shorter pathway to citizenship as older undocumented immigrants who were brought to the U.S. as minors.

Tougher Enforcement Triggers

Sen. Marco Rubio (R-Fla.) has said that the immigration bill that he helped write will not pass Congress without tougher border security standards. And his GOP colleagues on the Judiciary Committee took notice.

One of Ranking Member Chuck Grassley's (Iowa) 77 amendments would would require tougher border enforcement across all sectors, not just those areas deemed "high-risk," as the bill currently states. Another one of Grassley's changes would make it mandatory for employers to verify the immigration status of job applicants within 18 months of the bill's passage, years before mandatory screening is required in the existing bill.

Sen. Jeff Sessions (R-Iowa), who offered 49 amendments, wants 700 miles of reinforced fencing built along the southern border.

Republicans have long demanded that border security take priority over legalization in immigration reform. But even if these amendments pass, don't expect the skeptics to jump on board with the bill.

"If even the modest amendment I have offered fails, it is exceedingly difficult to see a way forward for this bill," Sessions said in a statement on Wednesday.

Tinkering With the Low-Skilled Worker Program

The Senate bill creates a program that would allow lesser-skilled immigrants to come to the country legally, with a starting point of 20,000 visas per year and the ability to expand to as many as 200,000. But the tug-of-war over the scope of the program isn't over yet.

An amendment by Sen. Mike Lee (R-Utah) would start the program out at 200,000 visas and allow it to grow to as many as 400,000 per year. That's more in line with the demands of business groups.

Some Democrats, on the other hand, would like to whittle the program down further. Sen. Chris Coons (D-Del.) put forth an amendment that would tie the start of the visa program to the security on the border, making sure border metrics are met before it starts.

Bringing Back Siblings

The Senate bill shifts the balance away from immigration based on family ties and toward a focus on employment. As part of that change, it cuts visas for siblings and married adult children of U.S. citizens.

Sen. Mazie Hirono (D-Hawaii) would bring those visas back.

And she doesn't stop there. Among her other family-based amendments, Hirono would allow legal permanent residents and citizens to bring two extended family members to the U.S. if they haven't brought other relatives.

Fallout From the Boston Bombing

Despite the chatter over immigration and the terror attacks in Boston, the Senate amendments don't do much to directly address them.

Sen. Lindsey Graham (R-S.C.) submitted a few amendments related to asylum and refugee law, including one that would cause you to lose your visa if you returned to your home country. Another Graham amendment would allow DHS to perform more extensive background checks on immigrants coming from regions that represent a "threat."